39 



(W) and Yankee (Y) signals or an errant LORAN-C receiver aboard the M/V Nancy G. 

 caused inaccurate TD readings, resulting in an apparent offset in the plot (Figure 4-3) of 

 disposal points. These 21 barges represent 36,391 m 3 of cap material that was released 

 between February 14 and March 8, 1990. The dredged material was derived from the 

 Connecticut Department of Transportation Project, during construction of the Baldwin Bridge 

 in the Connecticut River. 



Five stations from the 1990 REMOTS® survey at NL-85 were directly comparable to 

 the survey done in August 1988. These stations (N200N, NCTR, N200S, N200W, and 

 N200E) encompassed the central region of the mound. The OSI values and apparent RPD 

 measured at Station N200N were indeterminate in both surveys, so only 4 stations actually 

 could be analyzed. The depth of the mean apparent RPD increased from 3.0 cm in 1988 to 

 3.7 cm in 1990, and the OSI increased from +8.7 (1988) to +9.3 (1990). These differences 

 were not statistically significant, probably due to the small sample size. Nevertheless, the 

 direction of change in both indicators was consistent with expectations for an area recovering 

 from disturbance. 



4.3 Oxygen Concentration and Benthic Habitat Quality 



The objective of the CTD/DO sampling was to assess near-bottom dissolved oxygen 

 concentrations at the disposal site and reference stations and to consider these results in 

 relation to benthic habitat conditions at the site. Salinity, temperature, and sigma-t profiles 

 showed little stratification in the vicinity of the New London Disposal Site (see Appendix). 

 In the absence of a strong pycnocline, bottom waters will generally remain well oxygenated. 

 Oxygen concentrations measured 1 m above the bottom at the disposal site, and reference 

 stations were uniformly 8.3 mg-T 1 . The oxygenated bottom water was consistent with the 

 presence of well-developed oxidized surface layers of sediment at the disposal site and 

 reference stations (Figure 3-14). Surface oxygen concentrations were slightly more variable, 

 ranging from 7.9 to 8.9 mg-1" 1 . The results of the present (1990) survey suggest that oxygen 

 concentrations were uniformly high across the region and confirmed the prediction that 

 oxygen levels would be similar both on and off the disposal site. 



Monitoring Cruise at the New London Disposal Site, June-July 1990 



